Remarks on the Liechti-Strenner's examples having small dilatations

We show that the Liechti-Strenner’s example for the closed nonorientable surface in \cite{LiechtiStrenner18} minimizes the dilatation within the class of pseudo-Anosov homeomorphisms with an orientable invariant foliation and all but the first coefficient of the characteristic polynomial of the action induced on the first cohomology nonpositive. We also show that the Liechti-Strenner’s example of orientation-reversing homeomorphism for the closed orientable surface in \cite{LiechtiStrenner18} minimizes the dilatation within the class of pseudo-Anosov homeomorphisms with an orientable invariant foliation and all but the first coefficient of the characteristic polynomial $p(x)$ of the action induced on the first cohomology nonpositive or all but the first coefficient of $p(x)(x\pm 1{)}^2$, $p(x)(x^2\pm 1)$, or $p(x) (x^2 \pm x + 1)$ nonpositive.